Acid rain occurs in the midwest including major portions of the Corn Belt. Studies to date have suggested minimal yield response of field corn (Zea mays L.) to acid rain. However, small but significant reductions in yield have been shown for some cultivars under extreme conditions. To define further these yield changes this study examined the effect of simulated acid rain on parameters associated with corn yield. Cultivars 'B73 × Mol7' and 'Pioneer 3377' were shielded from ambient rain by two movable rain exclusion shelters. Six simulated rain treatments (pH 5.6, 4.6, 4.2, 3.8, 3.4, 3.0) were applied biweekly within these shelters through the use of a nozzle distribution system. For the most part growth and yield parameters were unaffected by simulated rain treatment. Analysis of 2 years of data for 100-seed dry weight, dry matter production, cob weight, barren plants and seed protein content indicated no significant trends (α≤0.05) with treatment pH for either cultivar. However, when contrasted with all other treatments, a small yield reduction (α≤0.05) observed at pH 3.0 for B73 × Mo17 (6%) was associated with a similar reduction in ears (5%), cob dry weight (5%), kernels per ear (3%) and slightly increased (3%) seed protein. Thus, while the only significant yield reduction was a contrast of pH 3.0 and the average of all other treatments for B73 × Mo17, this reduction appears to be the result both of slightly fewer ears and slightly less successful ear fill.
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Acknowledgements Although the research described in this article has been funded wholly or in part by the United States Environmental Protection Agency through cooperative agreement No. 810725-01 with the University of Illinois, it has not been subjected to the Agency's required peer and policy review and, therefore, does not necessarily reflect the view of the Agency, and no official endorsement should be inferred.
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